The long-term aim of this project is to determine the relationship between temporal processing deficits apparent in the brainstem response to complex acoustic cues and speech perception difficulties in noisy backgrounds. The specific objective of the proposed research is to characterize the brainstem encoding of speech and other complex stimuli in young and older adults. The proposed experiments are designed to compare younger and older listeners with near-normal audiometric hearing in order to understand how reduced fidelity of temporal processing affects encoding of the temporal components of speech and, consequently, speech perception. Aim 1 will employ auditory brainstem response measures elicited by speech as an index of periodicity coding. This study will test the primary hypothesis that the degree of periodicity coding measured at the level of the brainstem is dependent on stimulus duration. Aim 2 will model temporal deficits exhibited in the aging auditory system by estimating a measure of 'internal noise' for the older adults. This study will rely on an evaluation of the brainstem response elicited by speech stimuli that has been corrupted using a temporal jitter model. Aim 3 will relate the electrophysiological measures to psychophysical and speech perception measures in young and older adults. Both the psychophysical task (detection of dichotic low-rate frequency modulation) and the speech task (modulation masking release) are designed to capture aspects of temporal processing. The training program involves strong mentorship in research design, especially in the domain of signal processing (stimulus generation, response analysis, etc.) and data analysis essential to the proposed research. Results will contribute to a more refined understanding of sub-cortical processing of speech sounds and the effects of temporal processing deficits on speech processing. The translational emphasis of this project is to optimize the use of complex-ABR measures for the assessment of clinical populations who experience difficulty perceiving speech despite audiometrically normal hearing. PUBLIC HEALTH RELEVANCE: Speech-evoked auditory brainstem responses have been used to investigate auditory processing in a variety of clinical populations. This project will advance our understanding of how these responses depend on the characteristics of the speech sound as well as on the integrity of temporal processing in the affected ear. Project results will have direct clinical relevance in terms of the use of speech-evoked auditory brainstem responses in the assessment of populations with speech perception difficulties.